1. Field of the Invention
The present invention relates to a variable-capacity swash plate type compressor used in, for example, an automotive air conditioning system.
2. Description of the Related Art
Known variable-capacity swash plate type compressors are disclosed in, for example, Japanese Unexamined Patent Publication No. 52-96407 and Japanese Unexamined Utility Model Publication No. 1-114988. The known-variable-capacity swash plate type compressors include a hinge mechanism for controlling the tilting angle of the swash plate to change the capacity of the compressor. The hinge mechanism K disclosed in the above described JUMP'988 is typically shown in FIGS. 6 and 7 of the attached drawings. The compressor includes a drive shaft 90, a swash plate 93, and a rotor 91. The swash plate 93 has a top dead center position T, located above the sheet of FIG. 6, at which the piston completes its compression stroke.
In this hinge mechanism K, the rotor 91 is attached to the drive shaft 90 on one side thereof and has an elongated hole 91a having a central axis S extending parallel to a plane passing through the axis O of the drive shaft 90 and the top dead center position T of the swash plate 93 and in a direction from an outer position to an inner position relative to the axis O of the drive shaft 90, as shown in FIG. 7. The elongated hole 91a includes extended walls which are straight in the direction perpendicular to the central axis S. A connecting pin 92 is slidably inserted in the elongated hole 91a, and the swash plate 93 is tiltably hinged to the connecting pin 92 via a bracket 93a. A wobble plate (not shown) can be slidably attached to the swash plate 93. Pistons are inserted in the cylinder bores, and piston rods are arranged between the wobble plate and the pistons.
In this compressor, the rotational movement of the drive shaft 90 is transmitted to the swash plate 93, for rotating the latter, by the hinge mechanism K and the rotational movement of the swash plate 93 is converted into a wobble movement of the wobble plate, whereby the rotational movement of the swash plate 93 is converted into a reciprocal movement of the pistons. Simultaneously, the hinge mechanism K functions to control the tilting angle of the swash plate 93 depending on the pressure in the crank chamber which is controlled by a control valve (not shown), to thereby change the stroke of the pistons to vary the capacity of the compressor.
During operation of the compressor, the tilting movement of the swash plate 93 and the wobble plate is regulated by the predetermined curvature of the elongated hole 91a, so that the top dead center position of the swash plate 93 does not change back and forth irrespective of the change in the tilting angle of the swash plate 93, and accordingly, the top clearance of the pistons at the top dead center thereof is maintained substantially at zero.
In this type of compressor, however, a suction force acts on a portion of the swash plate 93 (a right half portion in FIG. 6) that is located on the rear side from the top dead center position T in the rotational direction of the drive shaft 90 since a suction force acts on the pistons in the suction stroke, and a compression reactive force acts on a portion of the swash plate 93 (a left half portion in FIG. 6) that is located on the front side from the top dead center position T in the rotational direction of the drive shaft 90 since a compression force acts on the pistons in the compression stroke. Therefore, in this type of compressor, a portion of the swash plate 93 on the rear side from the top dead center position T in the rotational direction of the drive shaft 90 (hereinafter referred to a suction side) tends to move away from the rotor 90, while a portion of the swash plate 93 on the front side from the top dead center position T in the rotational direction of the drive shaft 90 (hereinafter referred to a compression side) tends to move toward the rotor 90.
In the compressor described in this prior art, the swash plate 93 is attached to the drive shaft 90 via a cylindrical sleeve (not shown) having pivot pins extending perpendicular to the axis O of the drive shaft 90 so that the swash plate cannot only slide relative to the drive shaft 90 but tilt back and forth. Therefore, it can be said that the swash plate 93 is prevented from being inclined relative to the rotor 91 right and left under the above described suction force and the compression reactive force.
However, the cylindrical sleeve and the pivot pins should have a little clearance to allow the swash plate 93 to move and tilt back and force relative to the drive shaft. Therefore, the swash plate 93 tends to be slightly inclined relative to the rotor 91 under the above described suction force and the compression reactive force (as depicted by the angle .alpha. in FIG. 6), so that the connecting pin 92 makes a point contact with the walls of the elongated hole 91a, as shown by the character "I" in FIGS. 6 and 7. The suction force and the compression reactive force are supported by the points "I".
The torque is transmitted from the drive shaft 90 to the swash plate 93 through the rotor 91 and the hinge mechanism K, and the torque is also supported by the points "I" if the swash plate 93 is more and less inclined relative to the rotor 91.
Therefore, in the conventional compressor, there is a possibility that an abnormal wear occurs in the hinge mechanism K which controls the tilting of the swash plate, during high-speed or high-load operation of the compressor, resulting in a shortened operational life. This problem also occurs in the compressor disclosed in Japanese Unexamined Patent Publication No. 52-96407. In addition, a similar problem also occurs when a spherical sleeve is used for tiltably and rotationally supporting the-swash plate for facilitating the manufacture of the compressor, and when hinge mechanisms are arranged on either side of the top dead center portion of the swash plate.
The assignee of the present invention then proposed Japanese Patent Application No. 5-81944 describing a compressor including a new hinge mechanism K having a pair of hinge elements. This hinge mechanism K is shown in FIG. 8 in the attached drawings. The hinge mechanism K includes a pair of support arms 81 and 82 extending rearwardly from a rotor 80 toward a swash plate 83 on either side from the top dead center position T (located above the sheet of FIG. 8) of the swash plate 83, and a pair of guide pins 86 and 87 having respective one ends attached to brackets 84 and 85 of the swash plate 83 on either side of the top dead center position T from the swash plate 83. Each support arm 81 or 82 has a circular hole 81a or 82a extending parallel to a plane passing through the axis O of the drive shaft 88 and the top dead center position T and in a direction from an outer position to an inner position relative to the axis O of the drive shaft 88. Each guide pin 86 or 87 has at its other end a ball 86a or 87a secured thereto, the balls 86a and 87a being identical in diameter to each other and fitted in the respective holes 81a and 82a of the support arms 81 and 82. A spherical sleeve 89 is attached to the drive shaft 88 to support the swash plate 83 thereon, the spherical sleeve 89 being slidable relative to the drive shaft 88 along the axis O thereof.
A problem arises even in this compressor, that a noise or a vibration occurs due to a change in the pressure in the cylinder bores (not shown).
In this compressor, there is a widthwise inevitable error .vertline.1.sub.1 -1.sub.0 .vertline. between the distance 1.sub.1 between the centers of the circular holes 81a and 82a and the distance 10 between the centers of the balls 86a and 87a, the widthwise error being likely to occur in the manufacturing process. In the assembly work of the compressor, it is necessary to accommodate this widthwise error .vertline.1.sub.1 -1.sub.0 .vertline., by following means EQU .vertline.1.sub.1 -1.sub.0 .vertline..ltoreq.(d.sub.1 -d.sub.0)
where d.sub.1 is the diameter of the circular holes 81a and 82a, and d.sub.0 is the diameter of the balls 86a and 87a. That is, in this compressor, the diameter d.sub.1 of the circular holes 81a and 82a must be comparatively greater than the diameter d.sub.0 of the balls 86a and 87a, to absorb the widthwise error .vertline.1.sub.1 -1.sub.0 .vertline.. Therefore, there is a considerable gap between the circular hole 81a or 82a and the ball 86a or 87a, and the relationship of the ball 86a or 87a to the circular hole 81a or 82a is a freely movable, loose, fit rather than a slidable fit.
In the thus assembled compressor, the resultant force of the suction force and the compression reactive force derived from the not shown pistons to the swash plate 83 changes in its magnitude and in its acting point depending on the change in the pressures in the cylinder bores. For example, when the compression ratio is higher, the acting point of the resultant compressive force exists at a position between the circular holes 81a and 82a, and in this situation, the resultant compressive force pushes forward both balls 86a and 87a which are thus received by the front surfaces of the circular holes 81a and 82a.
When the compression ratio is lower or the pressure in the crank chamber increases, the acting point of the resultant force is displaced to the compression side (approximately the left hand half of FIG. 8) and does not exist at a position between the circular holes 81a and 82a. Therefore, in this situation, the ball 87a and the circular hole 82a on the compression side works as if it is a fulcrum so that a rearward force acts on the ball 86a on the suction side. This rearward force is received by the rear surface of the circular hole 81a.
It is desirable that the circular holes 81a and 82a receive the force constantly by their front surfaces only or by their rear surfaces only, but the circular holes 81a and 82a receive the force alternatingly by their front and rear surfaces since the pressure in the cylinder bores always changes depending on the suction, compression and discharge operation of the compressor and the point of the resultant force changes depending on the cyclic change in the pressure in the cylinder bores. Therefore, if a clearance between the circular hole 81a and the ball 86a is such a value as to establish a freely movable, loose fit rather than a slidable fit, the clearance is excessive and noise or vibration occurs because the forward and rearward forces are alternatingly received by the front and rear surfaces of the circular hole 81a.
In addition, in the compressor including guide pins 86 and 87 with balls 86a and 87a attached thereto, and if the widthwise error .vertline.1.sub.1 -1.sub.0 .vertline.is accommodated by the minimum in the allowable range, that is, if the following relationship exists, EQU .vertline.1.sub.1 -1.sub.0 .vertline.=(d.sub.1 -d.sub.0)
the circular holes 81a and 82a are always in abutment with the points of the balls 86a and 87a on the front side and on the rear side thereof in the rotational direction, so the torque is transmitted from both circular holes 81a and 82a, both balls 86a and 87a and both guide pins 86 and 87 to the swash plate 83. In this case, if the swash plate 83 is inclined to the right or to the left due to the suction force and the compression reactive force as described above or the swash plate 83 is pushed by the compression reactive force, at least one of the guide pins 86 and 87 is subjected to a stress, and an endurance of the parts will deteriorate.